Oxidation of the primary alcohol groups of carbohydrates (and carbohydrate derivatives) leads to the formation of aldehyde (R′—CHO) and/or carboxyl (R′—COOH) groups.
The formation of aldehyde and carboxyl groups enhances the reactivity, versatility and solubility of the resulting compounds which, therefore, have a greater number of industrial applications (for example, in the food, textile and paper industries). As a result, there has been a great deal of interest in the development of methods allowing for the selective oxidation of primary alcohol groups. One such method involves the use of nitroxy radical mediators.
A number of nitroxy radical-mediated oxidation methods have been described in the art. Examples of such methods can be found in the following applications: WO00/50621A1, WO01/00681A1, US20030029588A1, and EP1077221A1.
Unfortunately, all of the existing methods have a number of disadvantages. Both US20030029588A1 and EP1077221A1, for example, require the use of environmentally hazardous halide compounds. The main drawback of existing methods, however, is their poor performance in terms of the quantity of carbohydrate substrate that can actually be oxidised at any one time. In both of WO00/50621A1 and WO01/00681A1, for instance, the amount of carbohydrate which can be added to the reaction mediums described is restricted to no more than 1 to 2% dry substance (more often than not, in fact, the dry substance levels do not exceed 0.05%).
Thus, for any useful quantity of oxidised carbohydrate to be obtained, very large amounts of reagent would be required and the amount of waste water produced would be considerable. It has been suggested, for example, that in order to increase oxidation levels, greater amounts of enzyme should be used. Not only would this undesirably increase reaction costs, but it has also been found to be ineffective. Accordingly, existing methods are neither economical, nor suitable for application on an industrial scale.
There exists, therefore, a need for an improved nitroxy radical-mediated oxidation process. The present invention provides such a process.